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Message-ID: <871quhdy3e.fsf@mpe.ellerman.id.au> Date: Tue, 19 Jul 2022 23:35:33 +1000 From: Michael Ellerman <mpe@...erman.id.au> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Sudip Mukherjee <sudipm.mukherjee@...il.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Kees Cook <keescook@...omium.org>, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, linux-kernel <linux-kernel@...r.kernel.org>, linux-hardening@...r.kernel.org Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check Linus Torvalds <torvalds@...ux-foundation.org> writes: > On Sun, Jul 17, 2022 at 9:41 PM Michael Ellerman <mpe@...erman.id.au> wrote: >> >> > li 4,254 #, >> >> Here we load 254 into r4, which is the 2nd parameter to memset (c). > > I love how even powerpc people know that "4" is bogus, and have to > make it clear that it means "r4". I wouldn't say it's bogus, I was just translating from asm to English :) But I agree it's preferable to use a proper register name rather than a bare integer. I never write asm using bare integers, I always use r4 or %r4, because as you say it's too easy to get mixed up otherwise. When looking at generated code I usually use objdump -d output, which uses the "r4" syntax. > It's not even an IBM thing. S390 uses perfectly sane register syntax, > and calls things '%r4" etc. as accepts that syntax if you tell it to. We use that syntax in some of our newer inline asm blocks. > The human-written asm files have those #define's in headers just to > make things slightly more legible, because apparently the assembler > doesn't even *accept* the sane names. I would like to switch to using %rX everywhere and get rid of those defines, but it's never seemed like it's worth the churn. We have ~48K lines of asm in arch/powerpc. cheers
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